1. Field of the Invention
The invention relates to a multiprocessor computer system for forming a picture from object elements which are defined in a hierarchic data structure, said system comprising a connection for a host processor in order to receive therefrom the data of the object elements for storage in an input memory, and a point processor system which is fed by the input memory in order to calculate from the data structure of the object elements the pixel data per picture for output on a connection for a display member.
2. Description of the Prior Art
The general state of the art is as described in the book by W. M. Newman and R. F. Sproull: Principles of interactive computer graphics, ISBN 0-07-046338-7, McGraw Hill, 1979. This book describes differently organized data structures inter alia on pages 137-142; a hierarchic data structure is shown in the FIGS. 10-11. Furthermore, on page 421, FIGS. 26-4, a multiprocessor system of the kind set forth is disclosed; this system comprises inter alia a central processor, a matrix multiplier and a display processor. Appendix I, pages 481-489, contains a survey of vectors and matrices. Pages 315-320 describe the formation and the use of so-called Bezier curves which will be described in detail hereinafter.
Object elements are to be understood to mean herein quantitative models of flat or spatial entities such as surfaces, bodies and complex structures. These object elements will be described in detail with reference to the FIGS. 1a-1e. The advantage of a hierarchic structure consists in that an object element which is situated at a lower level of the hierarchic structure can be simply modified without the entire structure being modified; moreover, it is also advantageous that object elements defined at a lower level can often also be used again at a higher level. The latter holds good for a two-dimensional reproduction situation where exclusively linear transformations occur in the rendering process. The host processor produces relative transformations between the object elements, such as relative or absolute positions. The host processor can also supply new object elements or remove existing object elements. It is a problem of the known technique that often it is first necessary to determine which part of the object elements is situated within the display window, i.e. the so-called "clipping". It will be demonstrated that in the procedures to be disclosed hereinafter clipping is performed only at the end of the treatment of the point in question, said point being temporarily considered as being the center of a system of coordinates. In a simple case the pixels can be generated synchronously with the scanning of the picture in the display member. The display member may operate, for example on the basis of a line-wise scanned television picture tube; however, it may alternatively concern a matrix of multicolor LED or plasma elements or an ink-jet printer. The invention is restricted to a completely scanned display member for each pixel. The invention notably does not concern so-called vector-generated pictures which entirely consist of written vector lines and in which the scanning sequence may be arbitrary.